The purpose of this research is to elucidate the mechanism by which maleylacetone cis-trans isomerase together with coenzyme glutathione (GSH) catalyzes cis-trans isomerization of maleylacetone and maleylacetoacetate. Previous studies in our laboratory have shown enzyme-bound GSH functions as a nucleophile in the enzymatic reaction whereby it adds reversibly to the carbon-carbon double bond undergoing isomerization. Current studies are focused on the role of the enzyme. Suicide inhibitors, resembling the substrate, are being designed and tested in an attempt to gain information about any nucleophilic groups that might be present at the active site. In addition the reaction of N-ethylmaleimide (NEM) with enzyme is being examined.